An explosion may be defined as a self-sustaining chemical reaction which rapidly expands into a much greater volume. The degree of destruction caused by such an event is significantly influenced by the pressure wave created by gas expanding therefrom. Such a pressure wave can be created by low explosives—wherein there is combustion or rapid burning of the explosive material (i.e. deflagration); or, by high explosives—wherein there is detonation of the explosive material itself. With deflagration, the reaction velocity is less than the velocity of sound (normally in the range of 600 to 1000 m/s) and the pressure wave created is measured in bars. Typically deflagration occurs with such explosives as black powder, smokeless powders, propellants and pyrotechnics. In contrast, with detonation a short duration, supersonic shock wave is produced and a longer lasting, significant gas pressure wave follows. The velocity of a detonation event is considered to be in excess of 1800 m/s. Typically detonation occurs with what are termed primary, and secondary explosives. Primary explosives are relatively easy to initiate (i.e. very sensitive) and include such materials as lead azide, lead styphnate, and diazodinitrophenol (DDNP). Secondary explosives are less easy to initiate (i.e. less sensitive—generally requiring a shock wave for their initiation) and include such materials as octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX), 1,3,5-triazacyclohexane (RDX), and ammonium nitrate based explosives.
Terrorists and illicit bomber or insurgent IED makers may obtain explosive materials legally, or fraudulently, or by theft from military or commercial sources—or by improvising and mixing together widely available oxidizers and fuels to create an explosive—such as the mixture of ammonium nitrate (AN), an oxidizer, and fuel oil, a fuel, to create the explosive ANFO. Fuel oil is universally available as is AN—as AN is produced in enormous quantities and sold world-wide for use as a fertilizer and as an ingredient in legitimate blasting agents. In fact, AN based devices were used in the 2011 bombings in Delhi and Oslo, and the 2013 Hyderabad, India blasts—as well as—in the Alfred P. Murrah Federal Building in Oklahoma City bombing in 1995. The Oklahoma City bombing involved an ANFO device containing 4,800 pounds (2,200 kg) of ammonium nitrate fertilizer, nitromethane, and diesel fuel mixture (a blast calculated to be equivalent to 5000 pounds (2,300 kg) of trinitrotoluene (TNT)).
Another readily available explosive material is urea nitrate (UN) fertilizer—which is itself classified as a high explosive (containing both the oxidizing and fuel moieties of a secondary explosive material). In fact, UN has a destructive power similar to AN explosives, with a velocity of detonation of about 11,155 ft/s (3,400 m/s)—about half of that of TNT. A 1,336 pound (606 kg) urea nitrate (UN) fertilizer based explosive device was used to attack the World Trade Center in 1993.
As stated above, AN is a widely available, easily purchased chemical—due to its common use as a fertilizer and as an ingredient in mining explosives. In fact, reportedly, about 65% of the reported 16,300 IEDs detonated in Afghanistan in 2012 contained AN. AN is generally produced/available as a prilled bead, i.e. a generally spherical particle, resembling small shot or BB's. Various prills have been developed—some nearly solid with relatively glossy surface for use in explosives (where handling and long storage characteristics are important)—some with relatively non-porous surface (that tends to dissolve slowly—for fertilizer purposes). However, regardless of the prill, there has been little international success in rendering the AN material inert or in significantly reducing its explosive potential for large illegal bombs—without materially impacting its ability to function as a fertilizer.
U.S. Pat. No. 3,366,468 to Porter, titled “Method of Desensitizing Fertilizer Grade Ammonium Nitrate and the Product Obtained disclosed and claimed a method of rendering fertilizer grade AN by adding 5 to 10% mono- and diammonium phosphate, or a mixture thereof, with potassium chloride or ammonium sulfate. It is now understood that phosphate additives do not prevent the ammonium nitrate from exploding, and in fact, the energy released from an explosive of the ammonium nitrate/phosphate mix may be even greater than the energy from pure ammonium nitrate. Furthermore, the ammonium phosphate additives can be easily removed from the ammonium nitrate/phosphate mix through the addition of calcium nitrate which in turn forms even more ammonium nitrate. Thus, it is clear that the phosphate additives do little, if anything, to increase the stability of ammonium nitrate or deter terrorist activity therewith.
Alternatively, calcium ammonium nitrate (CAN) fertilizer, also known as nitro-limestone, was developed, manufactured and sold as a non-detonable alternative to AN—CAN contains about 20 to 25% calcium carbonate (CaCO3). The calcium carbonate is slurried with ammonium nitrate to form CAN—which crystallizes as a hydrated double salt (5Ca(NO3)2.NH4NO3.10H2O). The calcium carbonate is a diluent—physically separating the AN components such that an explosive reaction will not be sustained. However, as reported by the U.S. military's Joint Improved Explosive Device Defeat Organization (JIEDDO), see https://www.jieddo.mil/content/docs/JIEDDO_HME_Tri-fold_v3.pdf, insurgents routinely use two alternative methods to process CAN-26 (26% nitrogen and 25% CaCO3 diluent) into an AN oxidizing agent for use in ANFO devices. In the first method, the very soluble AN is separated from the insoluble carbonate diluent in the CAN by dissolving the CAN in hot water and simply decanting concentrated AN solution. Alternatively, the CAN is ground into a fine powder, without extracting the inert carbonate, and then functionally used in place of pure AN in the explosive device (the grinding process eliminating the physical separation provided by the diluent). In either case, CAN is reprocessed into a functional home-made-explosive (HME) AN or AN equivalent material.
Therefore, there is a need in the art for a method to defeat any modification of non-detonable CAN fertilizer to render it usable in any home-made-explosive (HME) device—as an AN explosive component, while maintaining its functionality as fertilizer.